As for a portable electronic device provided with a connector used for connecting an external device to the portable electronic device, when a charging device is connected to the connector while the connector is wet with water, a large amount of electric current (hereinafter, “current”) flows into the portable electronic device, and a failure may occur in the electronic device. Thus, portable electronic devices are known with which a cap is provided for the opening of the connector, so as to prevent the connector from getting wet. However, the configuration where a cap is provided for the opening of the connector is troublesome.
To cope with these situations, as a first piece of related-art, a configuration is known by which the power supply to a circuit within a portable electronic device is stopped when the portable electronic device is detected to be in a wet state, so as to prevent failures of the portable electronic device, without having to provide a cap for the opening of a connector.
As a second piece of related-art, another configuration is also known in which a wet state of a portable electronic device is detected by detecting a short-circuit state of an existing terminal that is already provided in the portable electronic device, so as to be able to detect the wet state without having to enlarge the scale of the portable electronic device.
Some portable electronic devices that are recently on the market are provided with a connector (which hereinafter may be referred to as a “micro USB connector”) that is compliant with the micro USB specification, as a connector used for connecting an external device to the portable electronic device. Examples of terminals which a micro USB connector may have include: an “ID terminal”, a “ground terminal”, a “VBUS terminal”. The voltage value detected at the ID terminal fluctuates according to the resistance value of a connection terminal of an external device connected to the micro USB connector. Thus, the portable electronic device is able to identify the external device connected to the micro USB connector, according to the voltage value detected at the ID terminal. For example, the portable electronic device determines that an “external device A” is connected to the micro USB connector when the voltage value at the ID terminal is “X volts [V]”, whereas the portable electronic device determines that an “external device B” is connected to the micro USB connector when the voltage value at the ID terminal is “Y [V]”.
Related-art examples are described, for example, Japanese Laid-open Patent Publication No. 2004-235724 and Japanese Laid-open Patent Publication No. 2010-035036.
The voltage value at the ID terminal, however, not only fluctuates according to the external device connected to the micro USB connector, but also fluctuates when the micro USB connector gets wet with water. The reason is that a resistance value due to the water is generated between the ID terminal and the ground terminal when the micro USB connector gets wet with water. When the voltage value detected at the ID terminal when the micro USB connector is in a wet state happens to coincide with a voltage value corresponding to a specific external device, the portable electronic device mistakenly recognizes the wet state as a state where the specific external device is connected. Even when a charging device is connected as an external device while the micro USB connector is wet with water, when the portable electronic device is able to accurately detect the wet state, it will be possible to block the current flowing into the portable electronic device from the charging device. However, when the portable electronic device mistakenly recognizes the wet state as a state where a charging device is connected, a large amount of current will flow into the portable electronic device, and a failure may occur in the portable electronic device.